1. Field of the Invention
The present invention relates to a shock wave calculus destroying apparatus and, more particularly, to an apparatus for destroying a calculus which uses an ultrasonic imaging unit to position a calculus and confirm the destruction state of the calculus.
2. Description of the Related Art
Recently, in treatment of a renal calculus or a gallstone, a method of non-invasive treatment using a shock wave is popularly used. Typical examples of a shock wave generating source include underwater discharge, electromagnetic induction, and a piezo-electric device, which have individual features. Various methods are used for positioning a calculus at a focal point of a shock wave and for confirming the destruction state of the calculus. Especially, a method of generating a shock wave by using a piezo-electric device has an excellent feature. More specifically, no consumable is used, the intensity of the shock wave can be arbitrarily controlled, and the focal point can be controlled by controlling the phase of the drive pulse applied to a plurality of piezo-electric devices (e.g., Published Unexamined Japanese Patent Application No. 60-145131 and U.S. Pat. No. 4,526,168).
In the initial stage of development of an apparatus for destroying a calculus, positioning and confirmation of the destruction state were performed by using X-ray TVs in two directions (e.g., Published Unexamined Japanese Patent Application No. 62-94144). With this method, however, the patient and the operator can be exposed to X-ray radiation, and continuous monitoring cannot be performed in order to minimize the X-ray dose as much as possible.
In contrast to this, in order to perform positioning and destruction state confirmation, recently, a method using an ultrasonic imaging unit is often employed (e.g., Published Unexamined Japanese Patent Application No. 60-145131). According to this method, a location to install an ultrasonic probe is limited to the inside or outside of a shock wave generating source. Nevertheless, this system receives a great deal of attention as it does not cause X-ray exposure and it can perform continuous monitoring.
In particular, since the ultrasonic imaging unit is a semi-real-time image diagnosing unit, it can continuously monitor the state of a calculus. Since continuous monitoring is possible, even if the position of the calculus is deviated from the focal point of a shock wave due to a respiratory movement or body movement of the patient, positional deviation can be immediately confirmed, and radiation of the shock wave is stopped in such a case.
When the ultrasonic imaging unit is used in the medical application described above, it is especially significant to detect a small calculus of about 5 mm. For this purpose, in order to improve the resolution, a so-called multi-stage focus is used, or the number of scanning lines per frame is increased. In this case, a high-resolution image can be obtained over a wide range by decreasing the frame rate (repetition frequency of the ultrasonic image=frame count per second) of the ultrasonic imaging unit. The real-time characteristics of the ultrasonic imaging unit are sacrificed more or less.
Use of an apparatus for destroying a calculus having such an ultrasonic imaging unit in an actual clinical case will be described. A high-resolution image is required before detection of a calculus is started in order to obtain the position of the calculus on a screen displaying an ultrasonic image. Once treatment is started, the frame rate can be increased. This policy is applicable without any problem when a slow movement of a calculus such as a respiratory movement is to be monitored. However, if the high resolution of an image is achieved simply by decreasing the frame rate, the following problems arise. These problems will be described below.
The present inventors conducted the following experiment. In this experiment, a shock wave was radiated on a calculus placed in water to destroy the calculus. According to this experiment, when destruction of the calculus proceeded by shock wave radiation and small calculus fragments were started to be formed, the fragments were observed to jump in synchronism with shock wave radiation. This phenomenon is called a stone dance. A similar phenomenon was observed in destruction of a calculus in a human body. Accordingly, this stone dance can serve as effective information indicating the calculus destruction state. Since the stone dance, however, is a quick phenomenon, it was difficult to observe it on an ultrasonic image at a low frame rate.
In the apparatus for destroying a calculus of this type, a single radiation shock wave operation is insufficient in most cases and repetitive radiation over a multiple of times is usually performed. A radiation count until calculus destruction is completed varies depending on the type of the calculus, the figure of the patient, the depth of the location of the calculus from the body surface, the energy of the shock wave, and the like. Hence, to record and reserve a numerous treatment data is effective in appropriately setting the shock wave radiation count. It is indispensable in terms of improvement of the treatment efficiency and safety to grasp the treatment state as a treatment trend during treatment.
Regarding the treatment method, an erroneous radiation preventive treatment mode for radiating a shock wave once or continuously without damaging tissues around the calculus has started to be employed. An erroneous radiation preventive treatment mode is described in Published Unexamined Japanese Patent Application Nos. 60-191250, 61-149562, and so on.
The erroneous radiation preventive treatment mode is as follows. That is, when a piezo-electric device is used as a shock wave source, a fact that a wave reflected by the focal region of the shock wave can be received by the piezo-electric device is utilized. A weak ultra-sonic wave is transmitted and received by the piezo-electric device immediately before an intense shock wave is emitted. When an intense echo is received, it is determined that the focal region of the shock wave coincides with the calculus. When this determination is made, a shock wave is irradiated on the calculus.
This erroneous radiation preventive treatment mode cannot be applied to all patients, as an intense wave is not always reflected by the patient. If an intense wave is not reflected by the patient, first, shock waves are continuously radiated in accordance with the treatment mode. Along with the procedure of destruction, when an intense wave is started to be reflected by the patient, the erroneous radiation preventive treatment mode may be set in place of the treatment mode.
In an apparatus for destroying a calculus having a shock wave source using underwater discharge or a small explosion, a mode having a similar function to the erroneous radiation preventive treatment mode is provided in addition to the treatment mode for radiating the shock wave once or continuously. According to this mode, a shock wave is radiated only during the inspiration end period of the respiration so as not to damage the tissues around the calculus, or a shock wave is radiated in synchronism with the electrocardiogram. When this mode is set, a destruction treatment mode is sometimes changed to another destruction treatment mode during a single destruction treatment.
Regarding the destruction rate, the higher the destruction rate, the faster the treatment is completed naturally. When the destruction rate is increased, however, the patient feels pain, or the destruction pressure is decreased due to cavitation. Therefore, the rate must be changed to an optimum value on the basis of the judgement of the doctor.
In this manner, not only the destruction energy quantity (more particularly, the drive voltage of the shock wave source, e.g., the piezo-electric device, and the pressure of the shock wave) but also the destruction treatment mode and the destruction rate serve as significant factors in terms of the treatment efficiency and safety. However, the treatment trend of the conventional apparatus for destroying a calculus includes only the transition graph (the radiation count is plotted along the axis of abscissa) of the destruction energy and the patient data (e.g., name, age, patient's ID No., and name of the disease) which are insufficient to evaluate the treatment efficiency and grasp the safety.
According to the erroneous radiation preventive treatment mode described above, only an ultrasonic image or an X-ray image can be used to determine the destruction degree of a calculus, and such a determination is not so reliable. Thus, even if the apparatus has a function of radiating the shock wave only to the calculus, the shock wave can be radiated continuously even after destruction is completed. In this case, damage to the normal tissues around the calculus cannot be neglected, and the treatment time becomes longer than necessary. Inversely, if the dose of the shock wave is excessively small, another treatment section will be needed, and impaction of a large calculus fragment in an ureter may occur.